This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A032664 #11 Dec 16 2019 16:54:42 %S A032664 1,3,7,9,13,27,31,37,39,49,51,57,63,67,73,79,81,91,93,97,99,103,109, %T A032664 117,123,129,151,153,163,171,181,187,193,201,213,217,223,229,231,237, %U A032664 249,259,277,279,283,289,291,297,301,303,307,319,321,327,361,367,373 %N A032664 Digit '1' concatenated with a(n) is a prime. %H A032664 Seiichi Manyama, <a href="/A032664/b032664.txt">Table of n, a(n) for n = 1..10000</a> %t A032664 Select[Range[400],PrimeQ[10^IntegerLength[#]+#]&] (* _Harvey P. Dale_, Dec 16 2019 *) %K A032664 nonn,base %O A032664 1,2 %A A032664 _Patrick De Geest_, May 15 1998 %E A032664 Edited by _Charles R Greathouse IV_, Apr 24 2010